T Lymphocytes And Cell-mediated Immunity Flashcards
What is an antigen?
This is any part of an organism or substance that the body recognises as non-self.
What type of molecules are antigens usually?
They are usually proteins.
What are antigens part of?
They are part of the cell-surface membrane or cell walls of invading cells.
What triggers the production of an antibody as part of the body’s defence system?
The presence of an antigen.
Is phagocytosis specific or non-specific?
Non-specific
What are the key features of specific immune responses?
They are slower at first but they can provide long-term immunity.
What does the type of specific immune response depend upon?
The type of lymphocyte.
Where are lymphocytes produced?
In the bone marrow.
What produces lymphocytes?
Stem cells
What are the two types of lymphocyte?
B lymphocytes
T lymphocytes
Where do B lymphocytes mature?
In the bone marrow.
What type of immunity are B cells associated with?
Humoral immunity
Where do T cells mature?
In the thymus gland.
What type of immunity are T cells associated with?
Cell-mediated immunity.
What does humoral immunity involve?
This involves antibodies that are present in the body fluids, or “humour” such as blood plasma.
What does cell-mediated immunity involve?
This involves body cells.
Why can T cells distinguish invader cells from normal cells?
Phagocytes that have engulfed and hydrolysed a pathogen present some of the pathogen’s antigens on their own cell-surface membrane.
Body cells that are invaded by a virus present some of the viral antigens on their own cell-surface membrane.
How do T cells distinguish body cells from transplanted cells?
Transplanted cells from individuals of the same species have different antigens on their cell-surface membrane.
How do T cells distinguish cancer cells from normal body cells?
Cancer cells are different from normal body cells and present antigens on their cell-surface membrane.
What are antigen-presenting cells?
These are cells that have the ability to display foreign antigens on their surface.
What is the cellular response?
This is where T lymphocytes only respond to antigens that are presented on a body cell rather than to antigens within the body fluid.
What do the receptors on each T cell respond to?
A single antigen.
Are there lots of T cells or only a few?
There is a vast number of different types of T cell and each type responds to a different antigen.
Summarise the response of T lymphocytes.
Pathogens invade body cells or are taken in by phagocytes.
The phagocyte places antigens from the pathogen on its cell-surface membrane.
Receptors on a specific T helper cell fit exactly onto these antigens.
This attachment activates the cell to divide rapidly by mitosis and form a clone of genetically identical cells.
What do the cloned T cells do?
They develop into memory cells.
They stimulate the phagocytes to engulf the pathogens by phagocytosis.
Stimulate B cells to divide and secrete their antibody.
Activate cytotoxic T cells.
What do cytotoxic Y cells kill?
They kill abnormal cells and body cells that have been infected by pathogens.
How do cytotoxic T cells kill?
They produce a protein called perforin which makes holes in the cell surface membrane.
What problems do the holes in the cell-surfaces membrane create?
The cell membrane becomes freely permeable to all substances and the cell does as a result.
What is the action of T cells the most effective against?
They are most effective against viruses but the body cell has to be sacrificed (because viruses replicate inside cells) to stop the virus from multiplying and infecting more cells.
